Antimicrobial resistance in Escherichia coli isolates from turkeys and hens in Ireland

Sir, We read with interest the paper by van den Bogaard and colleagues relating to the antimicrobial susceptibility of Escherichia coli isolates from poultry. Since September 2000 we have been studying the antimicrobial susceptibility of E. coli isolated as pathogens from poultry flocks in two counties in Ireland. Isolates were obtained on culture of tissues or swabs from diseased or dead animals and referred to the Department of Bacteriology, National University of Ireland, Galway, for antimicrobial susceptibility testing. The identity of the isolates as E. coli was confirmed by API20E and antimicrobial susceptibility testing was performed by the disc diffusion method of the NCCLS. Susceptibility to 13 antimicrobial agents (Table) was determined, using E. coli ATCC 25922 as control. For isolates categorized as intermediate or resistant to ciprofloxacin by initial disc diffusion susceptibility testing, the ciprofloxacin MIC was determined by Etest. A total of 209 isolates of E. coli have been examined, 171 isolates from turkeys and 38 from hens (broiler and egg layers). The percentage of isolates susceptible, intermediate and resistant to each antimicrobial agent is outlined in the Table. The ciprofloxacin MIC for the five ciprofloxacinresistant isolates was in the range 6 to 16 mg/L. Like van den Bogaard et al., we observed a trend towards higher levels of antimicrobial resistance in turkeys, in which antimicrobial use is more common. Resistance to sulphonamides, trimethoprim and nalidixic acid were more common in E. coli originating from turkeys, and ciprofloxacin resistance, albeit at a low level of 2.9%, was observed only in E. coli isolates from turkeys. Our data differ from those of van den Bogaard et al. in a number of respects. The isolates were considered pathogenic and susceptibility test methods and interpretative Correspondence Journal of Antimicrobial Chemotherapy (2001) 48, 587–595